The government's surprise abolition of national tests for 14-year-olds yesterday drew deep dividing lines between primary and secondary schools as unions welcomed the scrapping of tests for older pupils while lamenting ministers' resolve to preserve the more controversial tests for 11-year-olds.

The decision won Ed Balls and his department praise from across the education establishment, but unions representing primary schoolteachers spoke of "bitter disappointment" that the reforms did not go further.

Mick Brookes, general secretary of the National Association of Head Teachers, said: "We are dismayed at the decision to keep the current test arrangements for 11-year-olds. This will mean that England's 10/11-year-olds will be the only children in the UK to be put under this pressure."

The National Union of Teachers urged Balls to end primary testing as well. The Conservatives welcomed the decision, saying it chimed with plans they had outlined. The Liberal Democrats also welcomed the government's "complete U-turn".

Every 11- and 14-year-old in England takes between five and seven hours of English, maths and science national tests, commonly known as Sats, over five days in May. In the past 13 years that one-week in the summer term has fundamentally reshaped how schools teach.

The tests are used to assess pupils' progress, inform parents of their child's achievements, feed into national league tables to show how individual schools are performing and rate the progress of the education system overall. Government targets for improving children's basic skills are measured by the Sats results.

The problem, according to teacher unions and the General Teaching Council, is in using one set of tests to meet all these requirements. Tests should be an independent assessment of pupils' abilities but if they are also an assessment of the school's reputation via the league tables, then that process becomes corrupted.

Teachers, under pressure to ensure their school moves up the league tables, narrow their lessons to "teach to the test". Unions say this has radically changed the nature of schooling.

Where once teachers could adopt the methods they felt were best to grab children's imaginations - particularly for teenagers at the troublesome age of 14 - now they have to focus on what they know will come up in the tests.

MPs on the Commons education committee this year described how testing "distorted" children's education as they are drilled to pass exams to improve schools' positions in league tables. A report by Cambridge University academics said Sats were contributing to a "pervasive anxiety" in children's lives.

Research suggests that initial improvements in results across England was probably down to schools getting better at tutoring pupils, rather than a real improvement in skills.

Headteachers also point out that while it is an immensely expensive system they have little faith in the results.

The tests have also become something of a rod for the government's back as they repeatedly miss ambitious targets to improve results. For 14-year-olds, a decade of improvements has been followed by four years of stalled progress.

This year's tests were disastrous after the American firm, ETS, buckled under the weight of delivering and marking 9.5 million papers. ETS's £156m contract was terminated and Balls admitted yesterday that the crisis had contributed towards the timing of the reforms.

New "single-level tests" are being piloted in around 400 schools. They are based on music exams whereby pupils enter the test when their teachers think they are ready.